1. Field of the Invention
The present invention relates to an optical disk device wherein the gain of the device is adjustable in accordance with the reflection light of a laser beam emitted to an optical disk, and an optical disk gain adjusting method employed in the device.
2. Description of the Related Art
DVD-RAM optical disks, for example, have both a data recorded region and unrecorded region. Since in the DVD-RAMs, a laser beam is reflected with different reflectances from the data recorded region and unrecorded region, when a tracking error signal or focusing error signal is detected, different types of gain adjusting control are performed depending upon whether the error detection region is the data recorded region or unrecorded region.
Specifically, in DVD-RAMs, the reflectance of a laser beam is lower in a data recorded region than in a data unrecorded region. Accordingly, during DVD-RAM gain adjustment, the gain of an error signal detected in the data recorded region is increased, while that of an error signal detected in the data unrecorded region is decreased (see Jpn. Pat. Appln. KOKAI Publication No. 2002-288848).
As described above, in conventional optical disk devices, when accessing an arbitrary address position on an optical disk, it is determined whether data is recorded at the position. If it is determined that data is recorded, the gain of the acquired signal is increased in accordance with the reflectance at the address position, while if it is determined that no data is recorded, the gain of the signal is decreased in accordance with the reflectance at the address position.
This gain adjustment method cannot be applied to an optical disk that has characteristics different from those of a DVD-RAM. If the same gain adjustment as in a DVD-RAM is performed in an optical disk in which a laser beam exhibits a higher reflectance in a data recorded region than in a data unrecorded region, the gain of the high-level signal acquired from the data unrecorded region is further increased, and that of the low-level signal acquired from the data recorded region is further decreased. This destabilizes servo control using a tracking error signal or focusing error signal, resulting in a read error.